Luminescent device, process, composition, and article

ABSTRACT

This disclosure relates to a luminescent device having a uniformly coalesced, transparent, luminescent silica glass target containing an activating amount of at least one selected rare earth oxide. This disclosure further relates to a luminescent process, a composition, and an article of manufacture.

United States Patent [191 Barber et al.

1111 3,855,144- [451 Dec. 17,1974

[ LUMINESCENT DEVICE, PROCESS,

COMPOSITION, AND ARTICLE [75] Inventors: Stephen W. Barber, Toledo,Ohio;

William F. Nelson, Port Washington, NY.

Related US. Application Data [60] Continuation of Ser. No. 41,455, May28, 1970, Pat. No. 3,634,711, which is a division of Ser. No. 841,690,July 1, 1970, Patv No. 3,527,711, which is a continuation-in-part ofSer. Nos. 355,248, March 27, 1964, and Ser. No. 355,251, March 27, 1964,and Ser. No. 355,253, March 27, 1964, and Ser. No. 355,407, March 27,1964, and Serv No. 355,408, March 27, 1964, and Ser. No. 355,409, March27, 1964, and Ser. No. 355,421, March 27, 1964, and Ser. No. 355,422,March 27, 1964, and Ser. No. 355,444, March 27, 1964, and Ser. No.355,445, March 27, 1964, and Ser. No. 355,469, March 27, 1964, and Ser.No. 355,470, March 27, 1964, and Ser. No. 355,471, March 27, 1964, saidSer. No. 841,690, is a continuation of SersNo. 641,264, May 25, 1967,which is a continuation-in-part of Ser. No. 355,248, and Ser. No.355,251, and Ser. No. 355,253, and Ser. No. 355,407, and Ser. No.355,408, and Ser. No. 355,409, and Ser. No.

355,421, and Ser. No. 355,422, and Ser. No. 355,444, and Ser. No.355,445, and Ser. No.

355,469, and Ser. No. 355,470, and Ser. No.

[52] US. Cl 252/30l.4 F, 106/5 2 [51] Int. Cl. C09k 1 /l 0, C09k 1/54,C03c 3/28 [58] Field of Search 252/3014; 313/92, 108

[56] 'References Cited UNITED STATES PATENTS 11/1937 Fischer 252/301.6 F

OTHER PUBLICATIONS deBoisbaudran, Sur quelques Nouvelles FluorescenceComptes Rendus, Vol. CX, No. 1, pp. 24-28.

57 ABSTRACT This disclosure relates to a luminescent device havingauniformly coalesced, transparent, luminescent silica glass targetcontaining an activating amount of at least one selected rareearthoxide. This disclosure further relates to a luminescent process, acomposition, and an article of manufacture.

I 3 Claims, 4 Drawing Figures PATENTEDBEEI 11914 7 V r 3,855,144

sum a 95 9 FIG. 3

E S g 5 p M \f/w 55? PPM Y 5 h 0 Q/AUELEA/Gfl/ or 0017 07; mun/mafia!PATENTEDDEC 1- 71914 FIG. 4

Al ppm 00 PPM 72 Zoo/ f- Ce 2 400 /Al/ELENGfi-l OF OUTPUT: M/M/M/GRO/UStions Ser. No. 355,248, Ser. No. 355,251, Ser. No.

355,253, Ser. No. 355,407, Ser. No. 355,408, Ser. No. 355,409, Ser. No.355,421, Ser. No. 355,422, Ser. No. 355,444, Ser. No. 355,445, Ser. No.-355,469, Ser.-No.

355,470, and Ser. No. 355,471 all of Mar. 27, 1964,

and a continuation of application Ser. No. 641,264, May 25, 1967, whichis a continuation-in-part of all 13 of the foregoing applications filedon'Mar. 2 7, i964.

THE INVENTION This invention relates to the preparation and use of novelglass compositions consisting essentially of silica and small effectiveamounts of at least one selected oxide ingredient.

More particularly, in accordance with this invention, a substantiallytransparent, uniformly coalesced, homogeneous glass is prepared byuniformly compactinga homogeneous,-anhydrous mixture consistingessentially I of finely-divided, substantiallypure, non-crystallinesilica and a small effective amount of at least one glassmodifying oxideingredient selected to impart'desir'ed characteristics to theglass, andthen heating the compacted mixture under vacuum at an elevated,nondivitrifying' temperature for a'period of time sufficient to obtainsubstantially complete, uniform coalescence and sintering of themixture.

A wide range of oxide ingredients may be selected for the practice ofthis invention depending upon the characteristics desired in the glassbody.

Typical ingredients include not by way of limitation the oxides of V,Cr, Mn, Fe, Co, Ni, Cu, Sb, Zn, P, B, U, Ti, Zr, Hf, W, Ta, Ag, Au, Pb,Bi, As, and the rare earths.

In accordance with one important embodiment of this invention, it iscontemplated preparing a novel, substantially transparent, homogeneous,luminescent glass having a luminescence output of high'intensity byuniformly compacting a homogeneous, anhydrous mixture consistingessentially of finely-divided, noncrystalline, substantially pure silicaand a small effective amount of at least one luminescent oxideactivator, and heating the compacted mixture under vacuum at anelevated, non-devitrifying temperature fora period of time sufficient toobtain substantially complete coalescence thereof.

A wide range of luminescent oxide activators or dopants is contemplatedherein including not by way of limitation oxides of Sn, Sb, Zn, Ni, V,Mn, U, Cu, Ag, As, and the rare earths.

It has been discovered that compounds of the rare earths areparticularly suitable for the practice of this invention. Moreparticularly, it has been found that luminescent glasses of highintensity output maybe prepared by using one rare earth selected fromlanthanum, cerium, praseodymium, neodymium, samarium,'europium,gadolinium, terbium, dysprosium, erbium, thulium, ytterbium, andlutetium alone or in combination with at least one other rare earthselected from lanthaeuropium, gadolinium, terbium, dysprosium,'erbium,-thulium, ytterbium, lutetium, and holmium.

Specific rare earth combinations contemplated herein include: e

l. La'and-at least one member selected from Ce, Pr, Nd, Sm, Eu, Gd, Tb,Dy,' Trn, Yb, and Lu.

2.-Ce and at least one member selected fromPr, Nd,

Sm, Eu, Gd, Tb, Dy, l-lo,'Er, Tm, Yb, and Lu.

3. Pr and at least one member selected from Nd,"Sm,v Eu, Gd, Tb, Dy,Ho,,Er, Tm, Yb, and'Lu.

4. Nd and at least one member selected fromSm, Eu, Gd, Tb, Dy, H0, Er,Tm, Yb, andLu. I i Y 5. Sm Land atleast one member selected from Eu, Gd,Tb,Dy,"Ho, Er, Tm, Yb,an cl Lu.

6. Eu andat least one me in ber'sel ected from 0111b. Dy, Ho, Er, Tm,Yb,'and Lu.

7; Gd'and atileastoneme r'nb'e'r selected from Tb, Dy,

Ho, Er, Tm, Yb, and Lu.

8. Tb and at 'least one member selected from Dy, Ho,

Er, Tm, Yb, and Lu.

9. D,'y and at least one memberselected from Ho, Er,

Tm, Yb, and'Lu. e 3

10. Ho and atleastone member "selected from Tm,

l1. Eraiidat least'one member selected from Tm, Y arid Lu. v

'12.'Tm and at least one 'r neniber se 'lected from Yb and Lu,

ln accordancewith another embodiment of this invention, it iscontemplated using a luminescent glass body (prepared by the novel 'process described here inbefore) as the target'ma terial. i

Luminescence is photon emission initiated by energy forms other thanthermal agitation.' -'Luminescence of a solid under excitation requiressuitable arrangement and pop ulation of the electronic energ levels initsv constituent atoms: properly situated electrons are excited tohigher energy levels under excitation, and emit photons upon theirspontaneous return tolowerlevels. Luminescent materials are usedcommercially in cathode ray tubes, particularly television :picturetubes, X-ray and radar screens, Oscilloscopes, electron microscopes,fluorescent lights, radiation'detection devices, and luminous markers,signs, and dials. i

Luminescence deviceherein means any apparatus or contrivance in which.energizing radiation is converted to luminescence emission; targetherein means the-mamicrons, and then deposited on a subs'tr'a te.Organic materials are often used as binders to obtain more uniformphosphor deposition, or as membrane coatings for the phosphor to providea surface which can be aluminiz ed. Several disadvantages attend theseprocesses comminution adversely affects luminescence efficiency of thephosphors; the phosphors inherent sensitivityto deterioration bychemical attack is enhanced by their large surface/volume ratio. whenpowdered; uniform contact among phosphor particles and with thesubstrate is difficult to achieve, and inadequate contact causes lightscattering which decreases effective output; phosphor coatings havelittle abrasion resistance, and binders used in their preparation aresubject to thermal deterioration; and, of course, product fabricationtechniques are limited to those which do not adversely affect thesensitive phosphor screens. In cathodoluminescence devices theexcitation current must be kept below levels, usually low, which damagethe phosphor. Also, the screen is usually opaque, and consequentlyresolution and definition of a projected image are relatively poor. Aknown process designed to overcome some of these problems involvesblending powdered phosphor in a frit, followed by fusion. The phosphordeteriorates under thistreatment, however and the inhomogeneity of theresultant glass causes objectionable scattering of emitted light.

The luminescence devices of the present invention overcome many of thesedisadvantages by employing a target comprising a glass body consistingessentially of silica and a metal or metalloid oxide wherein the oxideis preferably that of a rare earth element as described hereinbefore.Broadly, the glass body consists essentially of vitreous silica withsmall amounts of the aforesaid glass-modifying metal or metalloid oxide,tag. at least one rare-earth oxide, where the number of metal ormetalloid atoms per million silicon atoms is from 5 to 5,000.

These compositions possess the unique and advantageous properties ofvitreous silica, including high chemical durability and low. thermalexpansion with consequent resistance to thermal shock. The transparencyof silica allows transmission of a greater range of exciting radiationsthan other glasses and most crystals. lts optical transparency inparticularallows excellent resolution, definition, and contrast ratio,so that images remain visible at luminosity levels lower than thosewhich are adequate with commercial opaque phosphors; conversely, thevitreous silica host can withstand extremely high current densitywithout damage, allowing cathodoluminescence to achieve high luminosity.The silica-rare earth oxide glasses of this invention possessparticularly unique and unexpectedly bright luminescence, especiallycathodoluminescence, when excited as hereinafter described.

The vitreous silica-rare earth oxide glass bodies used in the devices ofthe present invention are prepared by novel procedures which comprise afurther aspect of this invention. Prior art methods for preparingvitreous silica and forming objects therefrom can be classified intothose which begin with crystalline silica and those which use vitreoussilica as a starting material. The formation of vitreous silica from oneof its crystalline forms has been carried out by fusion and bysintering. The fusion process requires temperatures above 1,7 C, theliquidus of betacristobalite.- The resultant melt is difficult tohandle. It has a high viscosity which causes it to retain dissolved andentrapped gases tenaciously, a high vapor pressure, and a strongaffinity for impurities which enhance an already pronounced tendency todevitrify during cooling. For these reasons, properties such astransparency or homogeneity are often sacrificed to avoid thedifficulties associated with prolonged high temperature treatments, andthe resultant products are allowed to retain partial crystallinecharacter.

Thus in the process described in US; Pat. No. 2,958,604, particulatecrystalline silica (quartz) on which cerium oxidehas been uniformlydeposited is heated momentarily to l,750 C to obtain a fused productwhich resists darkening on exposure to nuclear radiation. Undoubtedly,the product retains substantial crystalline character, since it has.been shown that to obtain truly vitreous silica in which all quartzstructure is obliterated, crystalline starting material must besubjected to long exposure to temperatures of l,800 to 1,900 C; see V.A. Florinskaya and RS. Penchenkina, Dokl. Akad. Nauk SSSR 85, I265(l952). When optically transparent completely vitreous silica is to beprepared from crystalline precursors, fusion must be effected atprolonged high temperatures; a typical process requires temperaturesnear l,850 C for 8 hours under vacuum, to remove from the melt bubbleswhich otherwise provide sites for initiation of devitrification duringcooling. Known sintering processes for converting crystalline silica topartially vitreous silica involve temperatures of about l,l00 to l,700C. The higher temperatures in this range allow faster glass formation,

but incur the problem of cristobalite crystallization, Y

which occurs at l,300 to 1,7 10 C. The difficulties involved insintering quartz to obtain vitreous silica are discussed at length inUS. Pat. No. 2,270,718.

Vitreous silica is available from sources other than its crystallineforms: particulate vitreous silica can be prepared by the hydrolysis orcombustion of suitable silicon compounds such as silicon halides andorganosilanes. The finely divided material thus obtained can becondensed directly upon a molten surface and immediately fused asdescribed in US. Pat. Nos. 2,188,12l and 2,272,342. Particulate vitreoussilica from these sources or that obtained by grinding fused silica canalso be employed to form .large vitreous bodies by slip castingtechniques which require firing at l,l00 to l,260C for about 1 to 4hours. The products are translucent or opaque, porous, and partlycrystalline; see J. D. Fleming, Am. Ceram. Soc. Bull., 40 (12), 748(1961). A similar process at slightly higher temperatures (l,200 tol,450 C) has been said to give transparent products (US. Pat. No.2,268,589). Processes which begin with particulate vitreous silica butrequire temperatures well above the fusion point of betacristobalite arealso known: British Pat. No. 524,442 (1940) specifies 1,800 to 2,l00 C;S. D. Brown, The Devitrification of High-Temperature Glass" (Thesis,

University of Utah, l957) suggests l,800 to l,900 C. i

The difficulties expected from silica melts at these temperatures havealready been noted.

We have now discovered a method for preparing homogeneous, opticallytransparent, vitreous silica bodies essentially devoid of crystallinestructure and voids, at

temperatures well below l,800 C, In particular, we

have discovered a method for preparing vitreous luminescent bodies whichconsist essentially of substantially pure, non-crystalline silica and arelatively lesser portion of at least one metal or metalloid oxide,especially a rare earth oxide.

Within the useful concentration range already set forth, e.g. 5 to 5,000atoms of metal or metalloid ion per million silicon atoms, a range of to2,000 atoms is preferred. Concentrations substantially below this rangefail to provide a convenient brightness level under energization byreadily obtainable means, and

concentrations substantially above this level lead to decreasedtransparency in the product.

In the particular embodiment of this invention wherein the vitreoustargets contains two or more metal or metalloid oxide luminescentactivators, e.g. rare earth oxides, the concentration of each activatorshould be at least 5 atoms, preferably at least 50 atoms, with the totalconcentration of all the activators not ex ceeding 5,000 atoms,preferably less than 2,000 atoms.

The vitreous of non-crystalline silica compositions of this inventioncontaining a rare earth oxide have been found to be bothcathodoluminescent and photoluminescent; in particular,photoluminescence is obtained when the compositions are energized byultraviolet rays. For example, in a specific embodiment of thisinvention, the glasses which contain lanthanum oxide or lanthanum oxideand an oxide of a rare earth selected from praseodymium, cerium,neodymium, samarium, eruopium, gadolinium, terbium, dysprosium, thulium,ytterbium, and lutetium, are cathodoluminescent, whereas thosecontaining lanthanum oxide or lanthanum oxide and an oxide or a rareearth selected from praseodymium, cerium, neodymium, samarium, europium,gadolinium, terbium, dysprosium, thulium, and ytterbiurn arephotoluminescent.

According to a further embodiment of the invention,

there are provided vitreous fibers of silica containing a luminescentactivator, e.g. a rare'earth oxide; and, optionally, at least anotherluminescent activator. In each of those embodiments pertaining to silicafibers, the broad and preferred concentration ranges are as statedhereinbefore.

' In a further particular aspect of the invention there are providedglass fibers of the foregoing description.

wherein the central core of the fiber is as before described, butwherein there is an outer sheath of vitreous silica containingsubstantially no luminescent activator, or at least containing severalorders of magnitude less luminescent activator than in the core.

The foregoing silica glass fibers containing luminescent activators-are, of course, also responsive to the same energizing radiations asthe bulk glasses, and can thus be used in various luminescence devices.However, the fibers containing the outer covering of vitreous silicacannot be used as cathodoluminescent fibers by bombardment through thesilica sheath, since the electrons will not sufficiently penetrate.However, they can be employed by bombardment on the end where theluminescent glass is exposed. The clad fibers, are, however, responsiveto ultraviolet radiation, since silica will pass ultraviolet lightthrough the sheath to the core.

According to a specific embodiment of this invention for preparingluminescent glass, there is provided a process for making a transparent,luminescent glass which comprises compacting a homogeneous mixture offinely divided vitreous silica and at least one rare earth oxide whereinthe number of rare earth atomsper million silicon atoms is from 5 to5,000,- to form a coherent body, and heating the body thus obtained atl,000 to l,750 C for a time of from about 1 minute to about 24 hours. Ina usual embodiment silica of particle size 1 to 5,000 millimicrons isused.

batch components is more assured when the silica particle size is small.Therefore, in apreferred embodiment, vitreous silica of particle size 10to 2,500 millimicrons is used. In a particularly preferred embodiment,vitreous silica of particle size 10 to 100. millimicrons is used. V v

Because the temperatures involved in the glass forming procedures ofthis invention are well below 1,800C, the viscosity of the vitreousmaterial remains high throughout; this prevents significant migration ofthe rare earth components, and favors their homogeneous distribution inthe products already described.

The ability to obviate migration of rare earth components during glassformation also allows formation of physically uniform glasses whichcontain, a sharp boundary between two areas, one of which contains arare earth not present in the other, by heating two or more pressedbodies of the type already described and which contain different rareearth components, while they are in contact, to form a glass. Theboundary can be a plane, or any other shapeto which the coherent bodiesof this invention can be formed. The resultant glasses are useful asdecorative materials since each sharply defined segment of, for example,a-rod, can contain a different rare earth or rare earths, and thereforeemit a different luminescence emission when excited by energizingradiation. These materials are also" herein described also allowspreparation of otherwise homogeneous vitreous bodies in which there is asharp change in concentration of a constituent rareearth The timerequired to effect glass formation at a given temperature, or thetemperature at a set time, with decreased particle size. Also,homogeneous mixture of across a predetermined boundary, by heating twoor more pressed bodies of the type already described and which containdifferent concentrations of the same rare earth component, while'theyare in contact, -to form a glass. These products are especially usefulin applications where luminescence emission of the same wavelength butvarying intensity is desired. i

The luminescent glass compositions of the present invention are usefulas lightsources in illuminating devices, signs, markers, etc. Theluminescence devices of the present invention are loscopes, etc. t

The starting material for the practice of thepresent invention is finelydivided particulate non-crystalline or vitreous silica, usually with amaximum dimension of about 5,000 millimicrons. This material can beobtained by grinding or otherwise comminuting fused vituseful as displaymeans, oscilreous silica, or by combustion or vapor phase hydrolysis ofslicon derivatives, particulary organosilanes and silicon halides. Thelatter process is preferable, particularly for the smaller particlerange, because communicating to obtain these sizes is laborious, andtends to in troduce impurities. The particle size depends upon theheating schedule to be followed and the particular desired properties ofthe product. Limitations on the use 7 of a certain particle size,temperature, and time to obtain a vitreous, transparent, luminescentproduct are best established by routine test, and cannot be set forthfor all possible combinations.

Preliminary treatment of the particulate vitreous silica to remove waterand organic impurities is conveniently carried out by heating at 700 Cfor about 12 hours, followed by about 2 hours at l,000 C, both stepsoptionally being carried out in a vacuum. Firing at 700 C removes about90 percent of the water-and, if in air, organic material, firing atl,000 C removes most of the remaining water. Water thus removed is thatwhich is present as chemisorbed water, i.e., as silicon-bonded hydroxylgroups on the surface of the starting material. Although the anhydrousparticulate silica thus obtained is subsequently contacted with water,as discussed below, rehydration by chemisorption is so slow that it doesnot take place under the conditions used; see A. C'. Makrides and N.Hackerman, J. Phys. Chem. 63, 594 (1959).

The substantially anhydrous material obtained from the drying procedureis treated with about l ml of water per gram of silica to obtain aslurry or paste which can be compacted. The liquid used need not bewater, since it is removed at a subsequent step, and serves merely as amedium in which to manipulate the silica; other liquids such as alcoholand acetone can be used with suitable modification of subsequent steps.The homogeneous addition of the small amounts of the oxide ingredientsource to the silica is conveniently carried out at this step. The oxidesource can be added in a form which is soluble in the liquid used, andsubsequently precipitated in the paste, thereby assuring homogeneousdistribution in the final product. When water is used to prepare theslurry, selected salts in aqueous solution can be added, and the oxideor hydroxide thereof precipitated by addition of base. The salt andprecipitant should be selected so that by products from precipitationare volatilized during subsequent heating.

The paste thus obtained is next evaporated to dryness, at about l00 C orslightly more when water is the continuous phase, to give a more densematerial than the original anhydrous powder. The compressed material ispulverized by any convenient means, usually by mortar and pestle or aball mill. To retain highest purity, the abrasive surfaces should be ofalundum or silica. The pulverized material is fired at about 700 C inair to remove organic impurities which may have been reintroduced sincethe initial purification, and to complete removal of the added water orother dispersing medium. Temperatures substantially above 700 C shouldnot be exceeded, since premature coalescence of the particles can occur.Usually about 30 minutes at 700 C is adequate, with increasing time forlarger quantities. The resultant dried powder is next treated with abouttwo or three drops of water or other suitable liquid per gram toincrease cohesion of the particles. The dampened powder is then formedby pressing, usually in a stainless steel or platinum mold for highestpurity. Only about 100 psig is required for forming, although higherpressures can be used. Care should be taken that compacting isrelatively uniform through the mass so the surface does not seal duringsubsequent firing, leaving bubbles in the interior of the body. Thepressed f ms can be left in the die during subsequent firing or removedif desired. The pressed forms are next subjected to temperatures ofabout 700 C under a vacuum of about 10." mm of mercury. The temperatureis slowly increased to about l,250 C, where it ismaintained for aboutthirty to sixty minutes. The time at l,250 C depends upon the particularsize used. In gencral, heating should be discontinued when the pressedform has shrunk about 40 percent along each linear dimension, and beforethe surface has a glazed appearance. The purpose of the vacuum isprincipally to avoid trapping bubbles and to keep the glass in itsessentially anhydrous condition. The final coalescence is next carriedout at temperatures up to l,750 C in a vacuum conveniently maintained atabout 10" mm of mercury. The time required for complete coalescencevaries with the temperature used, usually from about 24 hours at lowertemperatures to about 3 minutes at temperatures near l750 C. Theproducts thus obtained are vitreous. that is, they are substantiallydevoid of crystalline struc titre.

As used herein, the term substantially pure silica means silica which isat least 99 weight percent pure.

The silica used in the following examples had a particle size of 10 to20 millimicrons and is designated Cab- O-Sil 0, can be obtained fromGodfrey L. Cabot, Inc., Boston 10, Massachusetts; the manufacturer givesthe compositin on a total weight basis as:

Al 0;, 0.0 l 0% Fe O, 0.00 l "/0 0.00 Wr CuO-MgO 0.000% Na o 0.020% SiOby difference 99.968%

The various aspects of the invention will now be illustrated withlanthanum oxide and it is to be understood that the other rare earthoxides can be used in place thereof as described and illustrated in the13 parent applications listed hereinbefore under related applications.Likewise, other glass modifying ingredients may be substituted.

EXAMPLE 1 This example describes preparation of transparent,luminescent, silica glasses containing lanthanum oxide.

A. Vitreous silica of particle size 10 to 20 millimicrons was heated at700 C for 12 hours and then at l,000 C for about 2 hours. The materialthus obtained was mixed with aqueous lanthanum nitrate in a ratio of 10ml of solution per gram of silica, and a solute concentration selectedto provide 5 lanthanum atoms per million silicon atoms. Aqueous ammoniawas added to precipitate lanthanum oxide on the surface of the silica,and the resultant mixture was evaporated to dryness at 100 C. Theresidue was ground with a mortar and pestle, and the powder thusobtained was first heated at 700 C for 30 minutes, and then mixed withtwo drops ofwater per gram of solid. The resultant material was pressedin a platinum die at 100 psig to form a coherent cylinder about inch indiameter and inch high. The pressed form was dried at about 100 C, andthen heated at 1,250 C until the cylinder had shrunk about 40 percentalong each linear dimension. The product thus obtained was placed in theclosed end of a vitreous silica tube, whose interior was kept undervacuum, and this assembly was heated at 1,750 C for 3 minutes, whereuponthe silica tube collapsed around the cylinder as coalescence occurred togive a transparent, luminescent glass of silica and lanthanum oxide. Theluminescent glass thus obtained is surrounded by an envelope of purevitreous silica; the envelope is readily removed, if necessary, bygrinding.

B. The procedure of Example [A was repeated, except that a concentrationof I00 lanthanum atoms per million silicon atoms and a final coalescencetemperature of l,600 C for minutes were substituted for the conditionstherein described; the product was a transparent, luminescent glass.

C. The procedure of Example lA was repeated, except that a concentrationof 200 lanthanum atoms per million silicon atoms and a final coalescencetemperature of l,500 C for 40 minutes were substituted for theconditions therein described; the product was a transparent, luminescentglass. I

D. The procedure of Example 1A was repeated, except that a concentrationof 2,000 lanthanum atoms per million silicon atoms and a finallcoalescence temperature of l,400 C for 9 hours were substituted for theconditions therein described; the product was a luminescent glass.

EXAMPLE 2 This'example describes preparationof transparent,

luminescent, silica glasses containing lanthanumoxide,

and another rare earth oxide. I

The procedure of Example 1A was repeated, except that the aqueouslanthanum nitrate therein described was replaced with aqueous lanthanumnitrate and praseodymium nitrate in a concentration of solutes se lectedto provide 10 rare earth atoms per million silicon atoms; the productwas a transparent, luminescent glass. The procedure of Examples lA-D canalso be adopted by suitable changes apparent to those skilled in the artto provide transparent, luminescent glasses of silica, lanthanumoxide-and neodymium oxide; silica,

lanthanum oxide, and samarium oxide; silica, lanthanum oxide, andeuropium oxide; silica, lanthanum oxide, and gadolinium oxide; silica,lanthanum oxide, and terbium oxide; silica, lanthanum oxide, anddysprosium oxide; silica, lanthanum oxide, and thulium oxide; silica,lanthanum oxide, and ytterbium oxide; and silicca, lanthanum oxide, andlutetium oxide, wherein there are 100, 2,000, or 5,000 rare earth atomsper million silicon atoms and at least five lanthanum atoms per millionsilicon atoms.

EXAMPLES This example describes preparation of luminescence devices fromglasses made according to Examples 1 and 2.

A. Samples of glasses prepared according to Examples l and 2 wereemployed as target materials and irradiated with ultraviolet lightfiltered to obtain wavelengths of 2,537A, and 3,660A. Under theseconditions, glasses which contained lanthanum and optionally anotherrare earth gave the following results: lanthanum, weak greenluminescence at the shorter wavelength; lanthanum-praseodymium, redluminescence of bright intensity at the shorter wavelength and infraredemission; lanthanum-neodymium, infrared emission; lanthanum-samarium,light pink luminescence of weak intensity at the shorter wavelength,blood red luminescence of weak intensity at the longer wavelength, andinfrared emission; lanthanum-europium, light red luminescence of mediumintensity at the shorter wavelength, pink luminescence of mediumintensity at the longer wavelength, and infrared emission;lanthanumgadolinium, ultra-violet emission; lanthanum-terbium, lightgreen luminescence of bright intensity at the shorter wavelength, andgreenish luminescence of very weak intensity at the longer wavelength;lanthanumthanum-praseodymium, dark red luminescence of medium intensityand infrared emission; lanthanumneodymium, infrared emission;lanthanum-samarium, red luminescence of bright intensity and infraredemission; lanthanum-eu-ropium, orange luminescence of weak intensity andinfrared emission; lanthanumgadolium, ultraviolet emission;lanthanum-terbium, blue green luminescence of very bright intensity;lanthanum-dyprosiu'm, yellow luminescence of bright intensity, andinfrared emission; lanthanum-thulium, dark blue luminescence of mediumintensity, and infrared emission; lanthanum-ytterbium, infraredemission; lanthanum-lutetium, ultraviolet emission.

EXAMPLE 4 This example describes the preparation of a transparent,luminescent glass of silica and rare earth oxides, which possessesseveral boundaries on one side of each of which the glass contains arare earth notpresent on the other side.

Vitreous silica of particle size 10 to 20 millimicrons was heated at 700C for l2 hours and then at l,000 C for about 2 hours. The material thusobtained was mixed with aqueous lanthanum nitrate in a ratio of 10 ml ofsolution per gram of silica, and a solute concentration selected toprovide 100 lanthanum atoms per milllion silicon atoms. Aqueous ammoniawas added to precipitate lanthanum oxide on the surface of the silica,

and the resultant mixture was evaporated to dryness at C. The residuewas ground with a mortar and pestle, and the powder thus obtained wasfirst mixed with two drops of water per gram of solid. The resultantmaterial was pressed in a platinum die at 100 psig to form acoherent'cylinder about inch in diameter and /3 inch high, heredesignated Sample A. The following samples were similarly prepared,substituting the designated rare earths for the lanthanum of Sample A:Sample B, 200 atoms of samarium per million silicon atoms; Sample C,atoms of lutetium per million silicon atoms; Sample D, 100 atoms oflanthanum and 100 atoms of praseodymium per million silicon atoms. The

pressed form was dried at about 100 C, and then heated at l,250 C untilthe cylinder had shrunk ajbout 40 percent along each linear dimension.The samples thus obtained were stacked in alphabetical order in avitreous silica tube, and the tube, whose interior was kept undervacuum, was heated at l,750 C for 3 minutes, whereupon the silica tubecollapsed around the cylinders as coalescence occurred to give atransparent, luminescent glass which was physically homogeneous and hadsharp boundaries between successive regions containing lanthanum;samarium; neodymium and lutetium; and lanthanum and praseodymium EXAMPLE5 This example describes the preparation of a transparent,-luminescentglass of silica containing lanthanum oxide, which possesses severalboundaries on one side of which the concentration of lanthanum isdifferent from that on the other side.

By the procedure of Example 4, a series of five samples was preparedcontaining, respectively, five, 100, 200, 300, and 400 lanthanum atomsper million silicon atoms. The resultant samples were coalesced asdescribed in the cited example to give a transparent, luminescent glasswhich was physically homogeneous and had sharp boundaries betweensuccessive regions containing lanthanum in the cited concentrations.

In particular, the luminescence spectra of the silicalanthanum oxideglasses of this invention show a broad continuum from about 400 to about520nm (nanometers). The spectra of the silica glasses of this inventionwhich contain lanthanum oxide and other rare earth oxide display thiscontinuum and, superimposed thereon, maxima at the following principalwavelengths; the term in parentheses is an approximation of relativeintensity: lanthanum-praseodymium 10.9nm (medium), 9l0nm (strong), 860nm(strong), 722nm (weak), 708nm (weak), 656mm (strong), 635mm (strong),612mm (strong), 592nm (weak), 490nm (weak); lanthanum-neodymium, 890nm(strong), 907nm (medium), ll0nm (weak); lanthanumsamarium, 566nm(strong), '78nm (weak), 605mm (strong), 65lnm (strong), 663nm (medium);lanthanum-europium 6l7nm (strong), 629nm (medium), 657nm (medium), 700nm(weak); lanthanumgadolinium 325nm (weak), 3l6nm (strong), 314mm(strong), 3l3nm (medium), 3llnm, 308nm, 306nm (weak); lanthanum-terbium377nm, 38lnm, 383nm, 4l3nm, 416mm, 420nm, 437nm, 440nm, 443nm, 459nm,474nm, 486nm, 54lnm, 548nm, 595nm, 630nm, 653nm; lanthanum-dysprosium582n m, 602nm (strong), 669nm, 67lnm, 678nm (medium), 758nm (strong),870nm (weak); lanthanum-thulium 458nm, 46lnm, 464nm (strong), 787nm;lanthanum-ytterbium 986nm (medium), 1,040nm (weak); lanthanumlutetiumca. 450nm.

EXAMPLE 6 A. The procedure of Example 1A was repeated, except thatpraseodymium nitrate, neodymium nitrate, samarium nitrate, gadoliniumnitrate, europium nitrate, terbium nitrate, dysprosium nitrate, holmiumnitrate, erbium nitrate, thulium nitrate, ytterbium nitrate, or lutetiumnitrate was used in place of the lanthanum nitrate. A transparent,luminescent glass of silica and the rare earth oxide was formed in eachinstance. The luminescent glass thus obtained is surrounded by anenvelope of pure vitreous silica; the envelope is readily removed, ifnecessary, by grinding.

B The procedure of Example 6A was repeated except that a concentrationof 100 of the aforesaid rare earth oxides per million silicon atoms anda final coalescence temperature of l,600 C for 10 minutes weresubstituted for the conditions therein described; the product was atransparent, luminescent glass.

C. The procedure of Example 6A was repeated, ex cept that aconcentration of 200 of the aforesaid rare earth oxides per millionsilicon atoms and a final coalescence temperature of l,500 C for 40minutes were substituted for the conditions therein described. Theproduct was a transparent, luminescent glass.

D. The procedure of Example 6A was repeated, except that a concentrationof 2,000 of the aforesaid rare earth oxides per million silicon atomsand a final coalescence temperature of l,400 C for 9 hours weresubstituted for the conditions therein described. The product was aluminescent glass.

EXAMPLE 7 The procedure of Example lA was repeated for each of thefollowing aqueous mixtures which were substituted for the aqueouslanthanum nitrate, and a transparent, luminescent silica glass wasobtained in each instance; praseodymium nitrate and neodynium nitrate;neodyium nitrate and samarium nitrate; samarium nitrate and europiumnitrate; europium nitrate and gadolinium nitrate; gadolinium nitrate andterbium nitrate; terbium nitrate and dysprosium nitrate; disprosiumnitrate and holmium nitrate; holmium nitrate and thulium nitrate; erbiumnitrate and thulium nitrate; thulium nitrate and ytterbium nitrate;ytterbium nitrate and lutetium nitrate. The concentration of solutes wasselected to provide 10 rare earth atoms per million silicon atoms. Theproduct was a transparent luminescent glass. 5

The procedure of Examples lA-lD can also be adapted by suitable changesapparent to those skilled in the art to provide transparent, luminescentglasses. of silica plus at least two of the aforesaid rare earth oxides.

EXAMPLE 8 A. Samples of glasses prepared according to Examples 6 and 7were employed as target materials and irradiated with ultraviolet lightfiltered'to obtain wavelengths of 2,537A. and 3,660A. Various resultswere noted, depending upon the particular rare earth oxides present inthe glass.

' B. Samples of glasses prepared according to Examples 6 and 7 wereemployed as target materials and bombarded with cathode rays. Again,different results were noted with respect to each glass, depending uponthe composition thereof.

The silica glasses of this invention which contain praseodymium oxideand gadolinium oxide possess remarkable and unexpected properties. Whenthese glasses are excited with ultraviolet radiation of wave. length2,537A, the emission spectrum of gadolinium is markedly enhanced.Quantitative intensity measurements are difficult, but it is estimatedthat the presence of praseodymium multiplies the intensity of gadoliniumluminescence by at least a factor of five. FIG. 1 shows a trace whichcompares the spectra obtained from glasses which contain gadolinium butnot praseodymium (lower curve) and glasses which contain gadolinium andpraseodymium (upper curve). The ordinate is proportionate to intensity.of emission under the same concentrations and excitation conditions foreach glass; it is apparent that the presence of praseodymium causessubstantial increase in brightness of luminescence emission. The causeof this synergistic enhancement of gadolinium emission by praseodymiumis unknown.

The present invention also provides new, substantially homogeneousglasses of silica containing europium oxide and terbium oxide whichpossess remarkable and Unexpected selective enhancement of theluminescence from certain electronic energy levels in terbium. Thusaccording to this aspect of the invention, addition of terbium andadjustment of the europium and terbium concentrations of the silicaglasses heretofore described can be used to enhance selectively certainwavelengths of terbium emission while others are substantiallyunaffected, and emission from europium is decreased. The causes of thisbehavior are unknown. A suitable rare earth concentration range for thesilica glasses of this invention containing terbium oxide and europiumoxide is from about to about 5,000 rare earth atoms per million siliconatoms, and at least five europium atoms per million silicon atoms.

The unusual and unexpected enhancement of certain terbium emissionwavelengths in the presence of europium is shown in FIG. 2, which is atrace of the luminescence spectrum of a glass of this inventioncontaining 2,000 terbium atoms and 200 europium-atoms per millionsilicon atoms, excited by 3,660A. ultraviolet irradiation; abscissaunits are nanometers. Since neither glasses containing europium but notterbium, nor those containing terbium but not europium gave measurablespectra under similar excitation conditions, it is apparent that amarked and unexpected enhancement of luminescence is provided by glassescontaining both of these rare earths. The causes of thissynergisticeffect are unknown.

The present invention also provides new, substantially homogeneousglasses of silica containing europium oxide a lutetium oxide which areremarkable and unexpectedin that they possess luminescence emissionspectra of unusual and unpredictable .wavelengths and intensities. Thus,according-to this aspect of the invention, addition'of lutetium andeuropium'can' be used to provide a silica glass containing europiumoxide and lutetium oxide which shows under suitable excitation a broademission continuum of high intensity from about 400nm to about 650nm(nanometers); this type of emission is not characteristic of eithereuropium or lutetium in the absence of one another. The causes of thissynergistic effect are unknown.

The unusual and unexpected spectra characteristic of the silica glassesof this invention containing europium and lutetium are represented inFIG. 3, which is a trace of the luminescence spectrum of a glass of thisinvention containing I00 europium atoms and 100 lutetium atoms permillion silicon atoms, excited by 3,660A. ultraviolet irradiation;abscissa units are nanometers. Since neither glasses containing europiumbutnot lutetium, nor those containing lutetium butnot europium gavemeasurable spectra under similar excitation conditions, it is apparentthat a marked and unexpected enhancement of luminescence is provided byglasses con-.

taining both of these rare earths; Also, the shape of the curve is notattributable to either rare earth. The causes of this synergistic effectare unknown.

The present invention also provides new, substan tially homogeneousglasses of silica containing terbium oxide and cerium oxide whichpossess remarkable and unexpected selective enhancement of theluminescence from certain electronic energy levels in terbium. Thusaccording to this aspect of the invention, addition of cerium andadjustment of the cerium and terbium concentrations of the silicaglasses heretofore described can be used to enhance selectively certainwavelengths of terbium emission while others are substantiallyunaffected, and emission from cerium is decreased. The causes of thisbehavior are unknown. A suitable rare earth concentration range for thesilica glasses of this invention containing terbium oxide and ceriumoxide is from about five to about 5,000 rareearth atoms per millionsilicon atoms, and at least five terbium atoms per million siliconatoms.

The unusual and unexpected enhancement of certain terbium emissionwavelengths in the presence of cerium is shown in FIG. 4, which is acomposite trace of the luminescence spectrum of a silica glasscontaining 200 cerium atoms per million silicon atoms, (lower curve),and the spectrum of a silica glass containing 200 terbium atoms and 200cerium atoms per million silicon atoms (upper curve) excited by 3,660A.ultraviolet radiation; the abscissa units are nanometers. Terbium undersimilar excitation shows no spectrum when similarlymeasured, and as FIG.4 shows, cerium in the absence of terbiumshows relatively weak intensityluminescence, whereas glasses containing both'show the relatively brightintensity spectrum characteristic of terbium shown as the upper trace inFIG. 4. The causes of this synergistic effect are unknown.

In particular, these principal wavelengths were observed in luminescenceof the silica glases of this invention'containing oxides of thefollowing rare earths; nm represents nanometers, and the term inparentheses is an approximation of relative intensity: terbium, 377nm,

440nm, 443nm, 459nm, 474nm, 486nm, 54lnm, 548nm, 595nm, 630nm, 653nm;terbium-dysprosium, 582nm, 602nm, (strong), 669mm, 67lnm, 678nm (me-.dium), 758nm (strong), 870nm'(weak), 377nm,

486nm, 54lnm, 548nm, 595nm, 630nm, 653nm; terbi- .um-thulium, 458nm,461mm, 464nm (strong), 787nm,

EXAMPLE 9 This example describes preparation of transparent,

. luminescent silica glasses containing terbium oxide-and cerium oxide,and their use as luminescence targets.

The procedure of Example 6A was repeated, except vide transparent,luminescent glasses of silica containing terbium and cerium oxides,wherein the number of rare earth atoms per million silicon atoms is fromfive to 5,000, and the number of terbium atoms per million silicon atomsis at least five. The glasses thus obtained show cathodoluminescence andphotoluminescence: when bombarded with cathode rays they show light blueluminescence of medium intensity; when bombarded with 2,537A.ultraviolet radiation they show light blue luminescence of mediumintensity; when bombarded with 3,66OA. ultraviolet radiation they showlight blue luminescence of bright intensity. Fibers drawn from theseglasses by conventional means gave similar results. ln particular,luminescence spectra of these glasses show an underlying continuum fromabout 4lOnm to about 600nm, attributable to cerium, with superimposedmaxima at 377nm, 38lnm, 383nm, 4l3nm, 4l6nm, 420nm, 437nm, 440nm, 443nm,459nm', 474nm, 486nm, 54lnm, 548nm, 595nm, 630nm, and 653nm,attributable to terbium.

As previously discussed, spectra of these glasses compared with those ofsilica glasses similarly prepared but containing terbium but not ceriumor cerium but not terbium at the same concentrations show decreasedintensity of luminescence attributable to cerium and an increasedintensity of certain wavelengths attributable to terbium, in particularthe maxima at 486nm, 54lnm, 548nm, 595nm, 630nm, and 653nm.

Although the examples hereof have been directed toward the use ofcertain rare earth oxides, it will be obvious to those skilled in theart that other rare earth oxide combinations can be used as well asother oxide ingredients, e.g. metal or metalloid oxides, including bothluminescent and non-luminescent activators.

The particular non-luminescent activator will depend upon the specificglass characteristics desired. Thus if one selects an oxide of cobalt(alone or in combination with other oxide ingredients), the resultingglass (prepared in accordance with this invention) will have hightemperature stability, low thermal expansion, unique filter properties,and unique sonic properties (for use in delay lines).

In preparing the mixture of silica and the oxide ingredient(s), theoxide may be used or it may be prepared by oxidation or hydrolysis asdescribed hereinbefore. When the latter technique is used, any source ofthe oxide cation can be used providing such source can be dissolved in aliquid suitable for wetting colloidal or otherwise finely divided silicaand subsequently precipitated onto the silica where it can be made toremain during the sintering and coalescing steps of the process withoutobjectionable chemical changes, e.g. such as the release of gas due to achange of valence.

It will be evident that modifications of this invention can be madewithout departing from the spirit and scope of this disclosure or thescope of the following claims.

We claim:

1. A substantially transparent, homogeneous luminescent glass consistingessentially of silica and oxides of the rare earths europium and terbiumwherein the total number of such rare earth atoms per million siliconatoms is from 10 to 5,000, and the number of each of said rare earthatoms per million silicon atoms is at least five, said silica glass,exclusive of said rare'earth oxides, being at least 99 weight percentsilica. 2. A substantially transparent, homogeneous, luminescent glassconsisting essentially of silica and oxides of the rare earths europiumand lutetium wherein the total number of such rare earth atoms permillion silicon atoms is from 10 to 5,000, and the number of each ofsaid rare earth atoms per million silicon atoms is at least five, saidsilica glass, exclusive of said rare earth oxides, being at least 99weight percent silica.

3. A substantially transparent, homogeneous, luminescent glasscconsisting essentially of silica and oxides of the rare earthspraseodymium and gadolinium, wherein the total number of such rare earthatoms per million silicon atoms is from 10 to 5,000, and the number ofeach of said rare earth atoms per million silicon atoms is at leastfive, said silica glass, exclusive of said rare earth oxides, being atleast 99 weight percent sil- UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent 3,855,144 Dated December 17, 1974 InVentor(S) StephenW. Barber et al.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Col. 4, line 3, "oxidehas" should read oxide has line 56, '1 800 Cshould read 1,800C.

Col. 5, line 23, "or" should read of line 67, after time," insertdecreases Col. 6, line 53, "slicon" should read silicon Col. 8 line 19delete "compositin on" and insert composi tion Column 9, line 13,"finall" should read final line 37, "silicca" should read H. silica Col.10 line 22 "dyprosium" should read dysp-rosium line 57, "ajbout" shouldread about Col. 14, line 25, "glases should read glasses Col l6 cl 3second line "cconsisting" should read 1.: consisting Signed and Sealedthis ninth Of December 1975 '[SEAL] Attest:

' RUTH C. MASON v C. MARSHALL DANN Alfefling ff Commissioner oflatentsand Trademarks FORM PO-IOSO (10-69) USCOMM-DC 60376-P69 UYS. GOVERNMENTPRINTING OFFICE: 9 930 v UNITED STATES PATENT OFFICE QERTIFICATE OFCORRECTION Patent No. 3,855,144 Dated December 17, 1974 n Stephen W.Barber. et a1 It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Claim 3, Column 16, line 34, "cconsisting" should read -consisting--.

Signed and Scaled this first Day of June1976 [SEAL] Arrest:

RUTH c. msou c. MARSHALL DANN Arresting Officer Commissioner nj'lalemsand Trademarks

1. A SUBSTANTIALLY TRANSPARENT HOMOGENOUS LUMINESCENT GLASS CONSISTINGESSENTIALLY OF SILICA AND OXIDES OF THE RATE EARTHS EUROPIUM AND TERBIUMWHEREIN THE TOTAL NUMBER OF SUCH RRARE EARTH ATOMS PER MILLION SILICONATOMS IS FROM 10 TO 5,00 SM
 2. A substantially transparent, homogeneous,luminescent glass consisting essentially of silica and oxides of therare earths europium and lutetium wherein the total number of such rareearth atoms per million silicon atoms is from 10 to 5,000, and thenumber of each of said rare earth atoms per million silicon atoms is atleast five, said silica glass, exclusive of said rare earth oxides,being at least 99 weight percent silica.
 3. A substantially transparent,homogeneous, luminescent glass cconsisting essentially of silica andoxides of the rare earths praseodymium and gadolinium, wherein the totalnumber of such rare earth atoms per million silicon atoms is from 10 to5,000, and the number of each of said rare earth atoms per millionsilicon atoms is at least five, said silica glass, exclusive of saidrare earth oxides, being at least 99 weight percent silica.